Accountability--the monitoring and use of student performance data to make judgements about school and teacher effectiveness--is increasing within school systems across the globe. In theory, by increasing accountability, the aims and incentives of governments, parents, school leaders and teachers become more closely aligned, potentially improving student achievement as a result. Yet, in practice, concerns are mounting about the stress that accountability is putting schools and teachers under. This paper presents new evidence on this issue, drawing upon data from more than 100,000 teachers across over 40 countries. We find evidence of a modest, positive correlation between school system accountability and how stressed teachers and headteachers are about this aspect of their job. When looking within schools, there is little evidence that the management practices of headteachers differ when they report feeling stressed about accountability, or that they transmit these feelings onto their staff. However, we do find strong evidence of 'emotional contagion' of stress amongst colleagues within schools, with teachers more likely to feel stressed by accountability if their colleagues do as well.